The present invention relates to a filter contaminant indicating system, and more particularly, to a temperature compensating device for use in a warning system which indicates when a hydraulic filter element should be changed because of contamination.
Tractors and similar types of machinery have plural hydraulic systems, and because of the environments in which they work, it is important to have the oil filtered and to know that the filters are clean and operative. A contaminated oil filter reduces the efficiency of the machine operation by restricting the flow of oil. Thus, it is important that the oil filter be functional for its intended use while permitting the maximum flow of fluid.
It is conventional to provide a device which automatically operates in response to a clogged hydraulic filter. Examples of prior art constructions are found in U.S. Pat. Nos. 2,879,892 and 3,482,696 which disclose warning lamps that are automatically operated in response to a clogged filter condition. Another prior art construction shown in U.S. Pat. No. 4,033,870, assigned to the assignee of the present invention, provides for the oil to be directed by a valve to one or more oil filters incorporated in the system, depending on the filter that becomes clogged. The latter system also provides a warning light which is activated to notify the operator that a filter is clogged and needs changing.
A problem with these prior constructions is that the indicator switch being used in present detecting systems is responsive to the pressure at the inlet to the filter, and no provision is made for changes in fluid viscosity as the fluid temperature increases. The warning light is on at colder temperatures because of increased fluid viscosity even though the filter may not be clogged. When the oil temperature increases and the fluid becomes less viscous, the warning light goes out. However, as the filter gradually becomes clogged because of contaminants, the temperature of the oil at which the light goes out correspondingly becomes higher. Thus, the operator must make a decision to change the filter based upon past observations as to the oil temperature at which the warning light went out. If different operators use the same machine, one or more of the operators may not know the oil temperature at which the warning light usually goes out, and the filter may be changed prematurely or after it becomes very clogged which defeats the purpose of a warning system.
The disadvantages of present filter restriction indicating systems have resulted in the temperature compensating device of the present invention which makes the warning system accurate in indicating when a hydraulic filter element should be changed because of contamination.